Editing Greenhouse (section)

== Theory of operation ==
The warmer temperature in a greenhouse occurs because incident [[solar radiation]] passes through the transparent roof and walls and is absorbed by the floor, earth, and contents, which become warmer. These in turn warm up the surrounding air within the greenhouse. As the structure is not open to the atmosphere, the warmed air cannot escape via [[Convection (heat transfer)|convection]] due to the presence of roof and walls, so the temperature inside the greenhouse rises.

Window glasses are practically transparent for short-wave infra-red radiation emitted by the sun, but almost opaque for long-wave radiation emitted by objects in the room.<ref>Koenigsberger et al. Manual of Tropical Building & Housing 1974 p102</ref>

Quantitative studies suggest that the effect of infrared radiative cooling is not negligibly small, and may have economic implications in a heated greenhouse. Analysis of issues of near-infrared radiation in a greenhouse with screens of a high coefficient of reflection concluded that installation of such screens reduced heat demand by about 8%, and application of dyes to transparent surfaces was suggested. Composite less-reflective glass, or less effective but cheaper anti-reflective coated simple glass, also produced savings.<ref>{{cite journal|url=http://uwm.edu.pl/wnt/technicalsc/tech_17_4/b04.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://uwm.edu.pl/wnt/technicalsc/tech_17_4/b04.pdf |archive-date=2022-10-09 |url-status=live|title= Energy Effects During Using the Glass with Different Properties in a Heated Greehouse|author= Sławomir Kurpaska|journal= Technical Sciences| volume= 17|issue=4 |date=2014|pages= 351–360}}</ref>

=== Ventilation ===
[[Ventilation (architecture)|Ventilation]] is one of the most important components in a successful greenhouse. If there is no proper ventilation, greenhouses and their growing plants can become prone to problems. The main purposes of ventilation is to regulate the temperature and humidity to the optimal level, and to ensure movement of air and thus prevent the build-up of plant pathogens (such as ''[[Botrytis cinerea]]'') that prefer still air conditions. Ventilation also ensures a supply of fresh air for photosynthesis and plant [[Cellular respiration|respiration]], and may enable important [[pollinators]] to access the greenhouse crop.

Ventilation can be achieved via the use of vents – often controlled automatically via a computer – and recirculation fans.

=== Heating ===
[[File:Greenhouse in Närpes.jpg|thumb|Thermal lights at a greenhouse in [[Närpes]], Finland]]
[[Heating]] or [[electricity]] is one of the most considerable costs in the operation of greenhouses across the globe, especially in colder climates. The main problem with heating a greenhouse as opposed to a building that has solid [[Opacity (optics)|opaque]] walls is the amount of heat lost through the greenhouse covering. Since the coverings need to allow light to filter into the structure, they conversely cannot insulate very well. With traditional plastic greenhouse coverings having an [[R-value (insulation)|R-value]] of around 2, a great amount of money is therefore spent to continually replace the heat lost. Most greenhouses, when supplemental heat is needed use natural gas or [[Electric heating|electric furnaces]].

Passive heating methods exist which seek heat using low energy input. [[Solar thermal collector|Solar energy can be captured]] from periods of relative abundance (day time/summer), and released to boost the temperature during cooler periods (night time/winter). [[Waste heat]] from livestock can be used to heat greenhouses, e.g., placing a chicken coop inside a greenhouse recovers the heat generated by the chickens, which would otherwise be wasted.<ref>{{Cite web |title=To Heat a Greenhouse, Add Some Chickens - GOOD |url=https://www.good.is/articles/to-heat-a-greenhouse-add-some-chickens |access-date=2023-09-18 |website=www.good.is |date=5 September 2011 |language=en}}</ref> Some greenhouses also rely on [[geothermal heating]].<ref>{{cite web|url=https://www.npr.org/sections/thesalt/2016/02/11/466050766/citrus-in-the-snow-geothermal-greenhouses-grow-local-produce-in-winter|title=Citrus In The Snow: Geothermal Greenhouses Grow Local Produce In Winter|website=[[NPR]]|date=11 February 2016 |last1=Gerlock |first1=Grant }}</ref>

=== Cooling ===

Cooling is typically done by opening windows in the greenhouse when it gets too warm for the plants inside it. This can be done manually, or in an automated manner. Window actuators can open windows due to temperature difference or can be opened by [[Electronics|electronic]] controllers. Electronic controllers are often used to monitor the temperature and adjusts the furnace operation to the conditions. This can be as simple as a basic thermostat, but can be more complicated in larger greenhouse operations.

For very hot situations, a [[shade house]] providing cooling by shade may be used.

===Lighting===
During the day, light enters the greenhouse via the windows and is used by the plants. Some greenhouses are also equipped with [[grow light]]s (often LED lights) which are switched on at night to increase the amount of light the plants get, hereby increasing the yield with certain crops.<ref>{{cite journal| pmc=4823311 | pmid=27092163 | doi=10.3389/fpls.2016.00448 | volume=7 | title=Nighttime Supplemental LED Inter-lighting Improves Growth and Yield of Single-Truss Tomatoes by Enhancing Photosynthesis in Both Winter and Summer | year=2016 | journal=Front Plant Sci | page=448 | last1 = Tewolde | first1 = FT | last2 = Lu | first2 = N | last3 = Shiina | first3 = K | last4 = Maruo | first4 = T | last5 = Takagaki | first5 = M | last6 = Kozai | first6 = T | last7 = Yamori | first7 = W| doi-access=free }}</ref>

=== Carbon dioxide enrichment ===
{{further|CO2 fertilization effect}}
The benefits of [[carbon dioxide]] enrichment to about 1100 parts per million in greenhouse cultivation to enhance plant growth has been known for nearly 100 years.<ref>Reinau, E. (1927) ''Praktische Kohlensäuredüngung'', Springer, Berlin</ref><ref>Brijer, C. J. (1959) "Een verlaten goudmijn: koolzuurbemesting". In: ''Mededelingenvan de DirectieTuinbouw''. Ministerie van Landbouw en Visserij, Nederland. Vol. 22, pp. 670–674</ref><ref>{{Cite book |author=Wittwer S. H. |date=1986 |chapter=Worldwide status and history of CO<sub>2</sub> enrichment – an overview. |chapter-url=http://agris.fao.org/agris-search/search.do;jsessionid=90899588119CF6294C561E8BD2D11019?request_locale=fr&recordID=US8733562&query=&sourceQuery=&sortField=&sortOrder=&agrovocString=&advQuery=&centerString=&enableField= |editor1=Enoch, H.Z. |editor2=Kimbal, B.A. |title=Carbon dioxide enrichment of greenhouse crops, Vol. I: Status and CO<sub>2</sub> Sources |location=Boca Raton, Fla. |publisher=CRC Press}}</ref> After the development of equipment for the controlled serial enrichment of carbon dioxide, the technique was established on a broad scale in the Netherlands.<ref>{{cite journal |last1=Wittwer |first1=SH |last2=Robb |first2=WM |year=1964 |title=Carbon dioxide enrichment of greenhouse atmospheres for food crop production |journal=Economic Botany |volume=18 |issue=1 |pages=34–56 |doi=10.1007/bf02904000|bibcode=1964EcBot..18...34W | s2cid=40257734}}</ref> Secondary metabolites, e.g., cardiac glycosides in ''[[Digitalis lanata]]'', are produced in higher amounts by greenhouse cultivation at enhanced temperature and at enhanced carbon dioxide concentration.<ref>{{cite journal | last1 = Stuhlfauth | first1 = T. | last2 = Fock | first2 = HP | year = 1990 | title = Effect of whole season CO2 enrichment on the cultivation of a medicinal plant, Digitalis lanata | journal = Journal of Agronomy and Crop Science | volume = 164 | issue = 3| pages = 168–173 | doi=10.1111/j.1439-037x.1990.tb00803.x| bibcode = 1990JAgCS.164..168S }}</ref> Carbon dioxide enrichment can also reduce greenhouse water usage by a significant fraction by mitigating the total air-flow needed to supply adequate carbon for plant growth and thereby reducing the quantity of water lost to evaporation.<ref>{{Cite journal |last1=Stacey |first1=Neil |last2=Fox |first2=James |last3=Hildebrandt |first3=Diane |date=20 February 2018 |title=Reduction in greenhouse water usage through inlet CO<sub>2</sub> enrichment |journal=AIChE Journal |doi=10.1002/aic.16120 |volume=64 |issue=7 |pages=2324–2328|bibcode=2018AIChE..64.2324S }}</ref> Commercial greenhouses are now frequently located near appropriate industrial facilities for mutual benefit. For example, Cornerways Nursery in the UK is strategically placed near a major sugar refinery,<ref>{{cite web |url=http://www.britishsugar.co.uk/tomatoes.aspx |title=Products and Services, tomatoes|access-date=10 July 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160624042707/http://www.britishsugar.co.uk/Tomatoes.aspx|archive-date=24 June 2016}}</ref> consuming both waste heat and CO<sub>2</sub> from the refinery which would otherwise be vented to atmosphere. The refinery reduces its carbon emissions, whilst the nursery enjoys boosted tomato yields and does not need to provide its own greenhouse heating.

Enrichment only becomes effective where, by [[Liebig's law]], carbon dioxide has become the [[limiting factor]]. In a controlled greenhouse, [[irrigation]] may be trivial, and soils may be [[Soil fertility|fertile]] by default. In less-controlled gardens and open fields, [[Keeling Curve|rising CO<sub>2</sub> levels]] only increase [[primary production]] to the point of soil depletion (assuming no droughts,<ref>{{cite web|date=23 April 2014 |last1=Buis|first1=A|title=NASA Finds Drought May Take Toll on Congo Rainforest |url=http://www.jpl.nasa.gov/news/news.php?release=2014-124 |website=Jet Propulsion Laboratory|access-date=17 May 2015}}</ref><ref>{{cite web|date=17 January 2013|last1=Buis|first1=A|title=Study Finds Severe Climate Jeopardizing Amazon Forest |url=http://www.jpl.nasa.gov/news/news.php?release=2013-025 |website=Jet Propulsion Laboratory|access-date=17 May 2015}}</ref><ref>{{cite journal |last1=Cook |first1=BI |last2=Ault |first2=TR |last3=Smerdon |first3=JE |title=Unprecedented 21st century drought risk in the American Southwest and Central Plains|journal=Science Advances|date=12 February 2015 |volume=1 |issue=1 |pages=e1400082 |doi=10.1126/sciadv.1400082 |pmid=26601131 |pmc=4644081 |bibcode=2015SciA....1E0082C}}</ref> flooding,<ref>{{cite news |last1=Marshall |first1=Claire |title=Global flood toll to triple by 2030 |url=https://www.bbc.com/news/science-environment-31738394 |access-date=17 May 2015 |agency=BBC |date=5 March 2015}}</ref> or both<ref>{{cite web |last1=Law |first1=Beverly |title=Carbon sequestration estimate in US increased – barring a drought |url=http://www.eurekalert.org/pub_releases/2011-04/osu-cse041411.php |website=www.eurekalert.org |publisher=AAAS |access-date=17 May 2015}}</ref><ref>{{cite journal |last1=Xiao |first1=J |title=Assessing net ecosystem carbon exchange of U.S. terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations |journal=Agricultural and Forest Meteorology |date=Apr 2011 |volume=151 |issue=1 |pages=60–69 |display-authors=etal |doi=10.1016/j.agrformet.2010.09.002 |bibcode=2011AgFM..151...60X |s2cid=5020848 |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1328&context=natrespapers}}<!--|access-date=17 May 2015--></ref><ref>{{cite journal |last1=Famiglietti |first1=J. |last2=Rodell |first2=M. |title=Water in the Balance|journal=Environmental Science |date=14 June 2013 |volume=340 |issue=6138 |pages=1300–1301 |doi=10.1126/science.1236460 |pmid=23766323 |s2cid=188474796 |bibcode=2013Sci...340.1300F}}<!--|access-date=17 May 2015--></ref><ref>{{cite web |last1=Freeman |first1=Andrew |title=Weather Whiplash: Texas Goes From Extreme Drought to Floods in 3 Weeks|url=http://mashable.com/2015/05/22/weather-whiplash-drought-flood/ |website=Mashable.com|date=22 May 2015 |access-date=30 May 2015}}</ref><ref>{{cite news |last1=Schwartz |first1=John |title=Scientists Warn to Expect More Weather Extremes |url=https://www.nytimes.com/2015/05/28/us/scientists-warn-to-expect-more-weather-extremes.html?_r=0|newspaper=New York Times |access-date=30 May 2015|date=27 May 2015}}</ref>), as demonstrated ''prima facie'' by CO<sub>2</sub> levels continuing to rise. In addition, laboratory experiments, free air carbon enrichment (FACE) test plots,<ref>{{citation | url=http://www.ns.umich.edu/new/releases/4007-soil-fertility-limits-forests-capacity-to-absorb-excess-co2 |title=Soil fertility limits forests' capacity to absorb excess CO<sub>2</sub> |date=18 May 2001}}</ref><ref>{{ cite journal |author1=Schlesinger, W. |author2=Lichter, J. |title=Limited carbon storage in soil and litter of experimental forest plots under increased atmospheric CO<sub>2</sub>| journal=Nature |volume=411 |issue=6836 |pages=466–469 |date=24 May 2001 |pmid=11373676 |doi=10.1038/35078060| bibcode=2001Natur.411..466S |s2cid=4391335}}</ref> and field measurements provide [[replicability]].<ref>{{cite journal |author1=Phillips, R. |author2=Meier, I. |title=Roots and fungi accelerate carbon and nitrogen cycling in forests exposed to elevated CO<sub>2</sub>| date=2012 |journal=Ecology Letters |doi=10.1111/j.1461-0248.2012.01827.x |pmid=22776588 |volume=15 |issue=9 |pages=1042–1049 |bibcode=2012EcolL..15.1042P |display-authors=etal}}</ref><ref>{{citation |first=Catharine |last=Richert |date=7 October 2009 |url=http://www.politifact.com/truth-o-meter/statements/2009/oct/07/plantsneedco2org/plantsneedco2org-claim-carbon-dioxide-not-pollutan/ |work=[[PolitiFact]] |title=PlantsNeedCO2.org claims that carbon dioxide is not a pollutant and is good for the environment}}</ref>